1. Field of the Invention
This invention relates to a print head for printing onto a printing medium patterns or images converted into electric signals.
2. Description of the Prior Art
Recently, office automation has required various terminals, among which a printing apparatus to convert electric signals into visible images, the so-called printer, has been in great demand so that the printing apparatus of various systems have hitherto been produced.
The printing apparatus using a metal paper or an electrosensitive paper comprising a vapor coated aluminum layer, a black layer and a substrate layer, allows an electrode to contact the vapor coated aluminum layer and applies a voltage to the electrode to remove the vapor coated aluminum layer by means of heating or discharge breakdown so as to expose the black layer for performing printing. Hence, in order to print an image of good quality, printing electrode styluses 11 are projected from a fixing member 12 as shown in FIG. 1-(A) so that the electrode styluses 11 are exactly in contact with a printing paper even after a long time use when the ends of the electrode styluses 11 are worn. In FIG. 1-( A), reference numeral 13 designates lead wires. The fixing member 12 is made of resin. In the case of the print head having electrode styluses not projecting but embedded in the resin as shown in FIG. 1-(B), the end of each of electrode styluses 14 is worn so as to often be out of contact with a printing paper, and the resin around each electrode is broken so that dust created in printing is deposited into the broken resin, resulting in the insulation between the electrodes being deteriorated leading to improper printing. In the case of the print head provided on a alumina (Al.sub.2 O.sub.3) substrate 15 (which is a hard substrate) with tungsten electrodes 16 as shown in FIG. 1-(C), the electrodes are worn so as to often be out of contact with a printing paper as described above, and since the alumina substrate of the fixing member is hard, it will injure the electrosensitive paper during printing, resulting in improper printing. Therefore, the projecting electrode styluses should be thick and hard and thus it is difficult to produce a multi-stylus print head and a print head enabling high resolution printing.
In order to solve the above described problems, a print head disclosed in U.S. Pat. No. 4,157,554 uses glass tubes providing passageways of fine wire electrodes which are fed by feed rolls to be compensated for wear of the ends thereof. With this print head, however, since the fine wire electrodes are protruded from the glass tubes, the diameter of each wire is limited, and the density of the wire electrodes cannot be increased.
U.S. Pat. No. 4,170,779 discloses a sheathed electrode in which the core is of hard material having a higher melting point (tungsten, for example) than the encasing material, the core being in contact with metal paper. However, although the diameter of the core is reduced, the density of the electrodes cannot be increased.
It is believed impossible to apply the above-described conventional print head to an elongated high density print head such as thermal printer.
Other recording systems, such as electrolytic electrography and electro-carbon-transfer printing (in the Journal of the Institute of Image Electronics Engineers of Japan Vol. 11, No. 1, P3.about.P9 (1982)), require the same print heads solving the above problems.